This invention relates to fluid-filled rotary dampers, in which a damping force is generated between two relatively rotatable parts by viscous friction in a fluid filling a space between the parts.
Fluid-filled dampers arranged for continuous rotation require a sliding or dynamic seal to retain the fluid within the damper. If, as is common, the seal is provided by an O-ring, for reliable sealing that O-ring is held under compression between inner and outer radial faces. This has the disadvantage that the pressure on the O-ring generates a significant sliding friction force when rotation occurs, and the level of that force tends to be unpredictable. It is possible to avoid the problem by using instead a moulded lip seal, but that is a relatively expensive solution.